1. Field of the Invention
This invention relates to an illuminatable touch contact and means for illuminating same for use with a manually actuatable short stroke sliding switch or key.
2. Description of the Prior Art
Use of so-called foil surface keys is known in the art to provide a flat operating surface in a field or bank with a plurality of touch contacts. Foil surface keys have a thin foil layer having a contact aperture which is sandwiched between two outer foil layers having metallic tracks. At an area aligned with the contact aperture, the tracks on the outer foil layers may be annular or planar. When the upper foil layer is lightly pressed against the lower, the interval between the outer layers is overcome and the contact is closed when the tracks meet at the contact aperture. The pressure required to make the contact is determined by the thickness of the intermediate foil. Upon release of the upper foil layer, that layer returns to its initial position because of its inherent elasticity and tension and the contact is again open. A switching symbol may be imprinted on the upper layer of foil, designating the function of the switch.
Foil surface keys such as the type described above have the disadvantage of a short life due to fatigue resulting from frequent actuation. When such fatigue occurs, the upper foil layer no longer returns to its initial position, resulting in a permanent contact. When such a permanent contact occurs, the entire control panel or bank of switches must be replaced, because the replacement of individual contacts is not possible in such a control panel configuration. Further, the tracks on the outer foil layers themselves may become brittle, resulting in intermittent circuits or complete failure.
Finally, space limitations make illumination from below of the switching symbol on the upper foil layer difficult and expensive.